Compared with the first-generation semiconductor of silicon and the second-generation semiconductor of GaAs, GaN semiconductor devices have many outstanding advantages such as large band gap, high electron saturation velocity, high breakdown voltage and ability to withstand high temperatures, which makes it more suitable for electronic devices operated under high temperature, high pressure, high frequency and high power. Thus GaN semiconductor devices have broad application prospects.
Since the GaN semiconductor devices are operated at the environment with high power and high current, a relatively large amount of heat is generated by the GaN semiconductor devices. Some performances of the GaN semiconductor devices are greatly influenced by temperature, for example, Schottky contact and carrier mobility, etc. If a local high temperature is generated within a Schottky contact region, the Schottky contact will be degraded, causing reduction of barrier height and increase of gate leakage current. In a severe case, the GaN semiconductor device will become failure. Even if there is no change of Schottky barrier at high temperatures, the energy of carriers in the GaN semiconductor device will increase as the temperature rises. In this case, the carriers are more likely to cross the barrier layer, thereby causing the increase of the gate leakage current. In addition, as the temperature rises, the phonon scattering suffered by Two-Dimensional Electron Gas (2DEG) in the channels increases, so the mobility of 2DEG rapidly decreases, causing a rapid decrease of the output current of the device. Therefore, the output power of the device is affected, thereby causing degradation of RF performance and microwave performance of the device. Thus it could be seen that effective heat dissipation has a significant impact on the reliability and performance of GaN semiconductor devices.
Currently, the GaN semiconductor devices dissipate heat in the following three ways: a part of the heat produced by the GaN semiconductor device is longitudinally transferred to a base of good thermal conductivity via a substrate; a part of the heat is laterally transferred to a passive region which is located outside an active region via metal electrode wires and semiconductor material inside the GaN semiconductor device; and a remaining part of the heat is dissipated through air above a top surface of the GaN semiconductor device. However, the cooling effect still needs to be increased in the art to further increase reliability and performance of the semiconductor devices.